The National Intelligence Service(NIS) says the North Korean troops deployed to Russia have temporarily retreated from the front lines and have not taken part in combat since mid-January.

The NIS on Tuesday confirmed a New York Times article dated January 30 mentioning that North Korean soldiers deployed to Russia had not been involved in combat for about two weeks.

The spy agency said their absence could be due to a significant number of casualties, adding that it is still investigating to learn more.

During a closed-door meeting of the National Assembly’s Intelligence Committee on December 13, the NIS reported that the number of casualties among North Korean troops deployed to Russia had exceeded three-thousand.

The New York Times, citing anonymous Ukrainian and U.S. government officials, reported that North Korean troops had suffered significant casualties and retreated from the front lines, adding that it was possible they would undergo additional training and be redeployed.